Thyratron actuated pawl circuit



Sept. 15, 1959 .1. B. RICKETTS, JR 2,904,726

THRYATRON ACTUATED PAWL CIRCUIT Filed March 4, 1955 FIG. I

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TIMF T INVENTOR. JAMES B. RICKETTS JR ATTORNEY United States Patent THYRATRON ACTUATED PAWL CIRCUIT James B. Ricketts, Jr., Bryn Mawr, Pa., assignor to Burroughs Corporation, Detroit, Mich., a corporation of Michigan Application March 4, 1955, Serial No. 492,060

4 Claims. (Cl. 317- 123) This invention relates to a method of and means for reading out numbers from computers and is more particularly concerned with an improved method of and means for stopping a print bar of a printing machine at a position representative of the number to be printed.

In the system with which this invention is concerned, a high speed electronic computer tells a printer when each number is coming up. The printer then senses each digit position to see which digitcoincides with the stated numher. The print bar position which corresponds to the coincident digit position is then stopped or selected at the right time with a solenoid actuated pawl. Accurate timing and fast operation for this procedure is critical. It is so critical that conventional solenoid actuation and release time for a pawl are not reliable.

An object of this invention is to provide an improved high speed solenoid operated device and method.

A more specific object is to provide solenoid actuation and release means using a thyratron which provides high speed functioning of pawls associated therewith.

In accordance with one feature of this invention a thyratron is connected into circuitry to drive a solenoid actuated pawl associated with each rack. Thyratro-ns which correspond to a coincident digit position are readied to fire by computer signals and then are fired synchronously at the time the pawl is to stop a particular rack from printer timing signals. The thyratron is connected in this invention to deenergize the solenoid when such stopping action is required, and provides for eliminating residual magnetism which inhibits fast operation.

In describing this invention in detail, reference will be made to the attached drawings wherein:

Fig. 1 illustrates mechanical details of a rack stop solenoid actuated in accordance with the invention;

Fig. 2 illustrates the thyratron circuitry coupled to actuate the rack stop pawl;

Fig. 3 illustrates an equivalent circuit for the thyratron and solenoid of Fig. 2; and

Fig. 4 is a graph of current in the solenoid upon firing the associated thyratron.

As shown in Fig. 1, rack 20 is provided with a stop or indent 21 for each position in which rack 20 is to be held against force F tending to move it to the left as shown. Solenoid and pawl assembly 22 has clapper 23 positioned to abut against a selected stop 21. Clapper 23 is urged in the direction of abutment by pressure from compressed spring 24. In an initial position solenoid 25 is energized, and pawl or clapper 23 is pulled down to be clear of stops 21. This energized position is the normal position of clapper 23. To stop the rack at a desired position, solenoid 25 is deenergized at the proper instant, allowing spring 24 to push clapper 23 into engagement with stop 21.

Fig. 2 shows a thyratron V1 connected to deenergize solenoid 25 when the thyratron is fired. The firing is accomplished in two steps. A digit coincidence from computer signals is sensed by and circuit 30, driving the cathode follower tube V2 to high current. This current raises the potential on the shield or No. 2 grid of 2,904,726 Patented Sept. 15, 1959 ICC? thyratron V1 from about -7 volts to slightly positive. Since it is desirable to trigger the thyratron from standard computer signals, capacitor 32 functions as part of an integrating circuit, holding lead 31 above ground potential for several milliseconds to permit functioning with trigger pulses of short duration. A further trigger input pulse is applied from the printer to grid No. l of thyratron V1 through the Fire terminal. Since this pulse is derived from a slower speed mechanical printer, it is of long enough duration to reliably trigger the thyratron. With grid No. 2 above 2 volts, a +5 volt pulse on grid No. 1 will trigger thyratron V1, and thus the thyratron itself serves as a logical and circuit for obtaining coincident timing.

When tube V1 fires, point 33 which has been at about +250 volts suddenly drops to about +10 volts. A strong negative pulse then passes through capacitor 34 to pawlactuating solenoid 25. This causes the current I initially flowing through the solenoid to decay rapidly, as shown in Fig. 4. When capacitor 34 is large enough, current I goes completely through zero and reverses. This negative current cancels the residual magnetism and allows clapper 23 to accelerate at the maximum capability of the pressure from spring 24. Thus much faster operation is possible by the combined features of releasing the clapper and cancelling the residual magnestim, so that operation of a high speed printer is possible.

Fig. 3 shows an equivalent circuit for the thyratron V1 and the associated solenoid circuit. When tube V1 fires, it is equivalent to switch 35 closing. This shunts solenoid 25 with charged capacitor 34 which pushes current through the solenoid in a direction opposite to current I from the +250 volt supply. With values as shown in Fig. 3, a negative current flows through solenoid 25 for a short period. Once pawl or clapper 23 engages stop 21, it will remain engaged until reset, even though current slowly returns to I, as shown in Fig. 4.

With the 220 K resistor in the thyratron anode circuit, the capacitor 34 coupling the solenoid to the thyratron anode holds the anode below volts during the time the tube deionizes after breaking the cathode circuit with the normally closed switch 60. This feature eliminates cathode-filament breakdown and permits the thyratron filaments to be coupled with other tubes.

In this manner, a thyratron actuates a relay by momentary deenergization and removal of residual magnetism, to provide high speed movement of clapper 23 to stop rack 20.

In the circuits of Figs. 2 and 3, the value of capacitor 34 in microfarads is chosen so that the electrostatic energy stored in capacitor 34 before thyratron V1 fires or switch 35 closes, is slightly greater than the electromagnetic energy stored in the magnetic field produced by current I through solenoid 25. Thus when tube V1 fires or switch 35 closes and capacitor 34 is effectively shunted across solenoid 25, deenergization of solenoid 25 occurs very rapidly because opposite and nearly equal energies are combining. The slight excess of energy in capacitor 34 drives a small reverse current through solenoid 25, removing residual magnetism.

Other embodiments of this invention will be evident from this illustrative description. The features of novelty provided by the invention are defined with particularity in the following claims:

What is claimed is:

l. A pawl actuation circuit comprising a voltage supply, a relay solenoid connected to said supply to store energy received therefrom, a capacitor connected to said solenoid and connected by an impedance element to said supply to store energy received therefrom, a gaseous discharge tube interconnecting said capacitor and said solenoid and effective upon firing to transfer the energy stored {is a) in said capacitor to =deenergize said solenoid, and input means connected to said gaseous discharge tube responsive to a plurality of signals to fire said tube.

2. A pawl actuation circuit comprising a source of electrical energy, a pawl actuating solenoid, a capacitor one plate of which is connected to said solenoid, separate resistance means connecting said source across said solenoid and across said capacitor and said solenoid in series to store energy therein, and a two grid gaseous discharge tube connected across said solenoid and said capacitor and effective upon firing to utilize the stored energy for rapid actuation of the pawl by said solenoid, said tube having a first input circuit responsive to coincident signals to prepare said tube for firing by raising one grid from low to high potential and having a second input circuit at the other grid responsive to a firing signal to fire said tube in the presence of the high potential at the first said grid.

3. Apparatus for rapid actuation of a pawl, comprising, a solenoid; a voltage supply; conductive means for connecting said voltage supply to said solenoid to pass current therethrough; a capacitor having one plate con nected to said solenoid; impedance means connecting the other plate or" said capacitor to said voltage supply to charge said capacitor by current flow through said impedance and said solenoid; a gaseous discharge tube having an anode, cathode, and a plurality of grid electrodes; means connecting said voltage supply to the anode-cathode electrodes of said tube; means for applying a plur-ality of signals to said grid electrodes of said tube to 4 fire aid tube in response thereto and thereby to discharge said capacitor through said solenoid.

4. A circuit for operating a relay solenoid comprising in combination, a source of energy connected for normally passing current through the solenoid including an impedance element connected between the solenoid and the source of energy, a capacitor coupled tosaid solenoid and having one plate connected to said source of energy for charging said capacitor, a thyratron having an anode, cathode and switching electrodes for selectively shunting said capacitor across said solenoid to discharge said capacitor thereby to reverse the current in said solenoid, an impedance device to couple the thyratron anode to said energy source, and a switch to couple the cathode to r effect deionization whereby the impedance device prevents cathode-filament breakdown upon deionization.

References Cited in the file of this patent UNI ED S E P TE 

